Steam assisted gravity drainage (SAGD) methods are commonly employed as an enhanced oil recovery technique for producing heavy crude oil and bitumen, especially in the oil sands projects. In this method, two parallel horizontal wells are drilled. The upper well injects steam into the geological formation, and the lower well collects the heated crude oil or bitumen that flows out of the formation along with water from the condensation of the injected steam. This condensed steam and oil are pumped to the surface wherein the oil is separated, leaving an oily/water mixture known as “produce water”. Roughly three barrels of this oily and bituminous containing process water are produced per barrel of recovered oil. Recovery and reuse of the water are needed to reduce operational costs and to minimize environmental concerns. The process water is eventually recycled to the steam generators used in the SAGD process, but it must first be clarified and separated from substantial amounts of suspended and emulsified oil, bitumen and other impurities like salts, silica, etc.
The SAGD produce water normally contains about 1-60% solids and has a temperature of about 95° C. It has accordingly been difficult to provide for effective clarification of this SAGD produced water.
Additionally, hydraulic fracturing or fracing may be used to initiate natural gas production in low permeability reservoirs and to restimulate production in older wells. These processes produce millions of gallons of so-called frac water. Once the fracturing is complete, the frac water is contaminated with petroleum residue and is returned to holding tanks for decontamination. Light non-aqueous phase liquids may be separated from the frac water via separation leaving an underlying contaminated frac water containing oily residue that must be separated prior to discharge of the water in an environmentally acceptable manner.